1. Field of the Invention
The present invention relates to a writing instrument, more specifically to a free ink type writing instrument in which an ink stored directly in an ink tank without absorbing a sliver or the like is fed to a pen tip from a temporary ink reservoir member.
2. Description of the Related Art
A member having a comb teeth-shaped cross section shown in FIG. 1 is known as a temporary ink reservoir member which is used as a flow controlling member of an ink in a free ink type writing instrument. Generally, such temporary ink reservoir member which has a much better wetting property to inks allows an ink to more easily flow between the comb teeth and therefore functions well as an ink reservoir.
Temporary ink reservoir members used for free ink type writing instruments which are commercially available in the market at present use ABS resins having good moldability, and it is proposed to add surfactants to inks containing water as a main solvent to control a surface tension of the inks or to subject temporary ink reservoir members to surface treatment such as plasma treatment and chromic acid mixture treatment to improve a wetting property to inks. However, satisfactory proposals to inks containing an organic solvent as a main solvent have not yet been made.
Organic solvents such as alcohols, glycols and glycol ethers tend to be used from a safety point of view in recent years. These organic solvents have a better wetting property to a temporary ink reservoir member than water because of their low surface tension, and in order to secure a satisfactory wetting property, a member having a larger critical surface tension is better used. In general, however, members having a large surface tension cause marked deformation and swelling with polar solvents such as alcohol and, in some cases they are dissolved therein and lose function as a temporary ink reservoir member.
Accordingly, it is considered to select materials having a relatively small critical surface tension to polar solvents such as alcohols for temporary ink reservoir members and to subject them to surface treatment including chromic acid mixture treatment and plasma treatment to thereby increase a critical surface tension on the surfaces of the members. However, not only the treatments themselves are complicated but also secondary steps for assuring the uniform treatment provided to the surfaces of the members are required.
Considering such situations, an object of the present invention is to provide a free ink type writing instrument in which an ink flows easily without subjecting a temporary ink reservoir member to specific surface modification and the member does not cause marked deformation and swelling with inks containing an organic solvent as a main solvent and in which temporary ink reservoir function works well.